Cabs mounted on construction machines adopt cab structures formed by pipe materials having hollow in the inside thereof as pillar members.
In the structures of the cabs mounted on the construction machines, the pipe materials used as the pillar members are required to have strength greater than or equal to a predetermined value. When thicknesses of the pipe materials are increased for enhancing strength of the pipe materials, however, this will be a factor of increasing cost such as material cost and processing cost. In response, a reinforcing structure has been demanded for solving both of the drawbacks in strength and cost.
For example, Japan Laid-Open Patent Application Publication No. 2006-321372 describes a cab having a structure that a coupling member is disposed at a joint section between a pillar member and a beam member for joining the pillar member and the beam member through the coupling member.